1. Field of the Invention
The present invention relates to blockage detectors, and in particular to blockage detectors that can be incorporated into air cooling systems to detect blockage in portions of the condensate drainage tubing.
2. Description of Related Art
U.S. Pat. No. 5,069,042 discloses a cleanable condensate trap that can be used in the condensate drainage tubing of an air cooling system. The cleanable condensate trap is designed so that any blockage existing in the trap can be easily detected and removed, for example, using a flexible brush that can be inserted through a U-shaped tube that forms part of the trap. A mechanical switching mechanism including a float can be included in a portion of the trap. The switching mechanism is arranged so that when liquid collects in the trap due to a blockage in the trap or in the tubing located downstream of the trap, the float rises so as to cause a mechanical switch to shut off the air cooling system and/or trigger an alarm. This prevents further liquid from collecting in the air handling system, which ultimately would overflow causing damage to dry wall, ceilings, walls, etc. in the building.
FIGS. 1 and 2 illustrate aspects of the cleanable condensate trap disclosed in U.S. Pat. No. 5,069,042. FIG. 1 is a diagrammatic view of an air cooling system incorporating the cleanable condensate trap of U.S. Pat. No. 5,069,042. The cooling system includes an air cooling device 2, for example, a central air conditioning unit or a heat pump. The air cooling device is operatively associated with an air handler 6, which includes heat exchange coils 4, that carry a cold material for cooling warm air conveyed to the air handler 6 through inlet duct 8. Cooled air is conveyed away from air handler 6 through outlet duct 10. As the air is cooled, liquid in the air condenses and is removed from the air and conveyed away from air handler 6 through tubes 12, 14 to, for example, a drain. The cleanable condensate trap 20 is located between the tubes 12 and 14, and provides a liquid seal between air located in air handler 6 and air located downstream of tube 14. The air cooling device 2 is controlled by, for example, a thermostat 16, which is electrically connected to the air cooling device 2 via a circuit 18. A switch 50 is operatively associated with the trap 20. Switch 50 opens circuit 18 when liquid in trap 20 rises to a predetermined level due to clogging of trap 20.
FIG. 2 is an exploded view of the switch of FIG. 1, and the structure for mounting the switch to a leg of a T-shaped tube, which forms part of the cleanable condensate trap 20. A microswitch holder/cover 83 removably mounts a microswitch 80 in a leg 24c of a T-shaped tube 24. Microswitch holder/cover 83 includes a holding portion 84, which removably attaches to microswitch 80 by, for example, the insertion of tabs 85 into holes 82 formed in the microswitch 80. Microswitch holder/cover 83 also includes cover portion 86, which extends outwardly from holder portion 84 a distance sufficient to entirely close the opening provided in leg 24c. An annular mounting portion 88 extends downwardly from cover portion 86 and is inserted into the opening in the leg 24c. For further details on the float structure, see U.S. Pat. No. 5,069,042, the disclosure of which is incorporated herein by reference in its entirety.
The above-described structure, however, cannot detect when the drain pan of the air handler or when the tubing located between the drain pan and the trap becomes clogged because liquid is prevented from reaching the U-shaped portion of the trap, and, thus the float is not actuated to open the microswitch. Additionally, it can be difficult to remove a clog from the pan and/or from the tubing between the trap and the drain pan with the cleanable condensate trap of U.S. Pat. No. 5,069,042. Accordingly, in such situations, the drain pan can become filled and overflow without detection by the sensor in the trap.
Occasionally a float malfunctions or ceases working properly because its mounting screws, linkages, etc. become loosened due to vibrations that the trap and associated tubing are subjected to during normal operation of the air cooling system.
Some jurisdictions require a secondary pan to be placed below the primary drain pan of the air handler in order to collect overflow that would occur when the primary drain pan or drain tubing becomes clogged. It is known to place a sensor (either a mechanical float or an electronic sensor) in the secondary drain pan to detect when liquid is overflowing from the primary drain pan to the secondary drain pan. These sensors can be float actuated or electronic.
It is also known to include float switches in the primary drain pan in order to detect when liquid in the drain pan reaches an undesired level due to a blockage.
However, it is necessary to open the air cooling unit in order to place the float or electronically activated switches in the primary or secondary drain pans, which can be difficult after installation. Additionally, these systems do not switch off the air cooling system when a clog is detected, but merely sound their own integrally-provided alarm, which can be difficult to hear, especially when the air cooling system is provided at a remote location of the building. If no one hears the alarm and/or if corrective actions are not undertaken in a timely fashion, so that the air cooling system continues to operate, water damage due to overflow from the primary or secondary drain pans can occur. Such systems also do not provide for easy access to the drain pan or to the drain tubing in order to remove the blockage.
Accordingly, it is desirable to eliminate the need for a secondary drain pan, and to avoid the possibility of the primary drain pan overflowing should it or any of the drain tubing become clogged.